The present invention relates to thermally operated valves and, more particularly, to a thermally operated valve (sometimes called a xe2x80x9cmodulatorxe2x80x9d) which automatically modulates the flow of fluids therethrough.
In the design, construction and operation of manufacturing, process and chemical plants, the control of fluid flow is a major concern to the design and operating engineer. It is also critical in environmental heating and cooling systems. The size and type of valves utilized at various control points result in a major portion of the cost of design and construction. In many applications it is desired to automatically control the flow of the fluid through a pipe, wherein the opening or closing action is effected directly by the temperature of the fluid flow being controlled. While one of the largest applications for this type of valve is the steam trap, there are many additional uses for valves of this type. For the purpose of clarification, the utility of the control valve of this invention will be described as it is applied to the steam trap application, but the control valves of this invention are not limited to that application.
In process or manufacturing plants, the steam trap provides an extremely important function. When operating properly and efficiently, it reduces the waste of energy and conserves heat energy in the system. However, when it is inoperable or performing inefficiently through corrosion, dirt, misuse, or simply through selection and installation of a valve of the wrong size or type, heat and energy losses are substantial. Steam, as it releases its heat units through process application, pipe radiation loss, or by other means, ultimately returns to its water or condensate state. If this condensate is not drained immediately or trapped from the system, it reduces the operating efficiency by slowing the heat transfer process and can actually cause physical damage to the equipment.
The condensate accumulates along the bottom of horizontal pipes and is swept along by the steam flow passing over it. Depending upon the volume and velocity, condensate may collect and fill the pipe, continuing to be swept along by the steam flow. If the velocity is sufficient, this water flow can do substantial damage to the equipment. It is therefore desirable in essentially all steam-operated systems to remove the condensate as often and as efficiently as is practically possible. The condensate typically forms and collects at elevation changes such as risers and expansion loops, at all low points and on long horizontal runs and, of course, ahead of all dead-end areas, such as shut off valves, pressure and temperature control valves and at the ends of steam mains. In particular it is important to remove condensate ahead of humidifiers, pumps, turbines and other equipment where water droplets may damage the equipment. In order to improve efficiency, steam traps are used downstream from heat exchangers, coils, unit heaters, cooking kettles, dryers, and the like. The temperature at which the condensate is discharged may be quite important to maintaining energy efficiency.
With all these various uses and positions for steam traps in the process system, and because of the physical and performance limitations on the various types of steam traps, many different types have been designed and marketed. While all of the many different types of steam traps operate by sensing the difference between steam and condensate, they may be classified as density operated (mechanical), temperature operated (thermostatic) and kinetic energy operated (disc and orifice). All of these various types have been necessary because of the limitations of the performance of the traps and not necessarily due to the result of the specific operating principle involved. Thus, although the device of this invention is temperature operated, it does not necessarily fall into the same category or have the limitations of the temperature operated steam traps presently available which include the balance-pressure thermostatic traps and the thermostatic traps which are characterized as liquid-expansion and bi-metal expansion traps. The operation, advantages, and limitations of these various types of traps are well known to process engineers and are described in Bulletin Number T-511 printed April, 1979 by Sarco Company, 1951 26th Street, S.E., Post Office Box 119, Allentown, Pa. 18105, entitled xe2x80x9cSteam Trap Selection and Application Guide,xe2x80x9d incorporated herein by reference. As will be clear from this xe2x80x9cGuide,xe2x80x9d the choice of the particular kind of trap is important for the application and needs of the particular situation.
The xe2x80x9cchoicexe2x80x9d problem relates not only to the type of trap, but also to the size of the trap, thereby requiring a thorough study of the rate of the expected flow and the characteristics of that flow before choosing the particular type and size of trap. These traps are expensive, complicated, and their selection involves a substantial portion of the total planning time in construction of a system. An incorrect choice of type or even size can result in poor performance or even complete lack of performance and could potentially damage equipment. Because of the nature of the device, it is common to use larger steam traps than necessary as they provide a substantial safety factor, and if the steam trap is found to be too small for the particular location, substantial expense and delay may be required before the system becomes operational. However, a trap having a capacity which is greater than system requirements may be energy inefficient and is certainly more costly. In addition, redundant systems are required because steam traps create notorious maintenance problems and are likely to need regular servicing. Strainer plugging is a common problem. As the steam trap ages, inefficiencies set in due to wear and due to deposition of various solids at the critical moving parts. It is common to fix or replace the steam traps in an entire system at regular intervals.
A particular problem with essentially all of the prior steam traps is determining how well the device is performing. In many applications, a substantial steam leak which results in energy losses cannot be easily detected. Such techniques as ultrasonic detection and other diagnostic tools are necessary to study the trap operation while xe2x80x9con stream.xe2x80x9d Many of the more costly and more efficient steam trap devices, however, are affected by particulates such as dirt or scale that might clog the working mechanism of the trap. This requires filtration upstream through the use of strainers and other such devices.
With the importance of energy conservation, particularly in process plant and boiler operations, even on a small scale, the steam trap and its efficient performance is a major concern. However, nothing has been offered as a satisfactory solution of various limitations of the presently available steam traps. These limitations include low thermal efficiency under varying loads and pressures, allowing steam loss during operation, the necessity of maintaining a water seal to avoid continuous discharge of steam, protection from freezing, limited discharge of condensate on a continuous basis, limited air venting capacity, inability to adjust the trap on-stream, limited use with super heated steam, on-stream damage due to water hammer, closure of the trap due to failure, protection from any steam impingement that might damage the equipment, failure to be self-adjusting to various pressure changes of the steam flow, requiring an open discharge outlet at the site of use, inconsistent operation particularly upon aging, being limited to low pressure operation, the design or construction requiring continuous steam bleed resulting in substantial waste even with light loads, use of mechanical parts which are subject to sticking, waterlogging of the flow system because of condensate holdback, and being limited to certain inlet pressures. These limitations are not present in all types of steam traps, but each type of steam trap suffers with some of these limitations and even the best choice leaves some disadvantages.
None of the prior art devices has provided a solution to the limitations of the steam traps and control valves as outlined above. Accordingly, it is an object of this invention to provide a control valve that operates on the principle of temperature increase in a fluid stream to control the rate of flow of that fluid. The present invention provides a steam trap that does not use a mechanical float or thermo-expansion of a bellows to close or open a machined orifice with a tapered plug. Accordingly, this invention provides a steam trap design that is not prone to wear, plugging, or substantial maintenance problems relating to internal components of typical steam traps. Furthermore, the present invention provides a trap that is not affected by or subject to freezing, due to the requirement of a condensate reservoir or the internal design of the device. The present invention also vents all system air, accumulated water and non-condensables as soon as possible and provides a cold port opening through the steam trap. The present invention also provides a flow path adequate to pass particulates and fluid surges without clogging or restriction of flow.
The present invention is multipurpose in nature, such that it may be used with a wide range of condensate flow rates, operating pressures, pipe sizes and system applications. Further, the present invention provides a trap with essentially no metal wear parts, and which is capable of insertion in-line and is compact in size by comparison with present steam traps. It is not limited to use as a stream trap, but may be used in any setting where a fluid flow must be modulated or controlled in response to an input temperature.
The present invention also operates such that cooler temperatures expand the orifice and increase flow through the trap to provide a quick and complete discharge of condensate liquid, particularly on start-up conditions. Unlike prior art devices, the present invention provides very rapid response to direct steam contact with the trap and to changes in the temperature of the flow generally. Further, the valve of the present invention provides a closure valve that will compensate for erosion of the inside surface to prevent leakage. For increased safety over prior art designs, the valve of the present invention will not remain in the closed position in the event of a failure, but will return to the open position. For increased economic efficiency, the valve of the present invention has a long performance life and will be less expensive to install and operate.
In our parent U.S. patent application Ser. No. 09/592,821, a valve is disclosed for automatically modulating fluid flow using a flexible flow adjustment member with a variable-diameter passage, an outer surface and a shell. The flexible flow adjustment member is made of an elastomeric material, preferably a VITON(copyright) elastomer. The shell surrounds at least a portion of the outer surface and creates a void between the shell and the outer surface. A thermally reactive material fills the void and contacts the outer surface of the flexible flow adjustment member. A substantial portion of the thermally reactive material is configured to change phase to vapor in response to an increase in temperature within the interior cavity to exert pressure on the flow adjustment member.
The present invention is directed to a valve for automatically modulating a flow of fluid through the valve, which is an improvement over the valve of U.S. patent application Ser. No. 09/592,821.
The valve comprises a flexible flow adjustment member having a variable diameter passage therethrough and an outer surface; a shell surrounding at least a portion of the outer surface and creating a void between the shell and the outer surface, the shell being in contact with the flow of fluid; and a thermally reactive material that expands when heated and contracts when cooled, the thermally reactive material being within the void and in contact with the outer surface of the flexible flow adjustment member for exerting pressure thereon in response to a heating of the thermally reactive material to cause a diameter of the variable diameter passage to decrease and to relieve pressure thereon in response to a cooling of the thermally reactive material to permit the diameter of the variable diameter passage to increase, the thermally reactive material comprising a substantially non-volatile heat transfer liquid that does not undergo a phase change in use, the liquid containing inert particulate filler.
In another aspect, the valve may be used for automatically modulating a flow of condensate from a steam system that includes steam at a saturation temperature. The flow of condensate is permitted to pass through the variable diameter passage at an average temperature that generally parallels the average temperature of saturated steam within the steam system within a range up to about 40 percent. The average maximum temperature of condensate flow permitted to pass through the variable diameter passage differs from the average minimum temperature of condensate flow permitted to pass through the variable diameter passage by up to about 25 degrees Fahrenheit.
In another aspect, the valve includes a housing having a wall defining an interior cavity. The valve also includes a modulator mounted within the interior cavity. The modulator includes a shell in fluid communication with the interior cavity and a flexible flow adjustment member within the shell. The flexible flow adjustment member has a variable diameter passage therethrough. The variable diameter passage is in fluid communication with the interior cavity. The modulator also includes a void between the flexible flow adjustment member and the shell and a thermally reactive material within the void and in contact with the shell for thermal communication therebetween.